This is kind of a thought-provoking card.
Normally you don't want to fail tests, because failing tests means you lose anything you contributed to the test (skills, resources, items, actions, etc.) in addition to suffering the consequences for failure. Does Take Heart make it worth failing a test?
I think failing a test is normally bad enough that it's not worth deliberately failing in order to get cards and resources. So, I don't think this card will see a lot of play on its own merit. However, I think it has good interactions with the following cards:
Calvin Wright is a natural fit for this card - his low stats guarantee that he is going to fail tests, and so using this card in the beginning will help him get his early-game engine going. Silas Marsh also may want this card because he can contribute it to a test and then pull it back to his hand using his ability if the test succeeds unintentionally. Lastly, Live and Learn can let you fail a skill test, collect the benefit of Take Heart, and then let you take the test again with more cards, resources, and a +2 bonus. That's really good.
I don't know if it's worth a card slot on its own - conventional wisdom is that playing cards to avoid failing tests altogether are normally better than cards that let you salvage something out of the failure - but there are some interesting interactions that I think make this card effective if it's used thoughtfully.